1. Field of the Invention
The present invention relates to a technique for preventing illegal copying of a document, and more particularly to a technique for controlling a copying operation for a document consisting of a plurality of pages with the use of a barcode.
2. Description of the Related Art
In order to prevent illegal copying of a document, the following method has been proposed: a copying condition indicating whether or not a document is “Copying inhibited” is embedded in the document as image data when the document is created, and then the document is printed out. On the other hand, when the document is copied, a copier detects the copying condition from the printed document, and controls the copying operation (performs the copying operation, or stops the copying operation) according to the copying condition.
For example, Japanese Patent Laid-Open No. 2004-336806 discloses a method in which a copier determines whether or not condition information such as a pin number is embedded in a document to be copied, and if the copying condition is embedded, only permits copying to a valid user by performing user authentication. Also, Japanese Patent Laid-Open No. 2002-305646 discloses a method in which a copier comprises a unit adapted to detect two-dimensionally coded information represented by a specific symbol (secret mark) and a secret level (diagonal pattern) from a document to be copied: if detecting the specific symbol, further detects the secret level; and controls the copying operation on the basis of the secret level. According to this method, it can be determined whether or not the document to be copied requires the control of the copying operation simply by determining whether or not the specific symbol is embedded in the document. Further, Japanese Patent Laid-Open No. 2001-245144 discloses a method comprising: reducing the resolution of a scan image to determine whether or not the image is likely to have a digital watermark; and if it is determined that the image is likely to have the digital watermark, determining whether or not the scan image having the document resolution has the digital watermark.
However, in the method disclosed in Japanese Patent Laid-Open No. 2004-336806, the condition information having a large amount of information has to be read every time the copying is performed, so that copy throughput is reduced. Also, in the method disclosed in Japanese Patent Laid-Open No. 2002-305646, the secret level (corresponding to the above condition information) is read out only if the secret mark is detected, so that copy throughput is high, which is different from the method disclosed in Japanese Patent Laid-Open No. 2004-336806. However, in the case of the method disclosed in Japanese Patent Laid-Open No. 2002-305646, the copier has to be designed to be able to perform the two operations, i.e., the detection of the secret mark and the extraction of the information from the two-dimensional code, and therefore the design becomes complicated. Further, in the method disclosed in the Japanese Patent Laid-Open No. 2001-245114, the processing for extracting the digital watermark present over the entire surface of the image must be performed twice, so that processing speed is significantly reduced.